What Causes the Toilet to Gurgle When I Let Water Out of the Bath Tub?
If your toilet gurgles when drain the tub, it doesn't mean there is something wrong with the toilet. The problem is probably a malfunction in plumbing pipes you might not even know about -- the vent pipes. Vents don't carry water the way drain pipes do but they are essential to a properly functioning plumbing system. A gurgling toilet is a sign that they're blocked, and leaving them that way could cause more serious problems. Does this Spark an idea?
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The Purpose of Venting
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All the drains in your house, including the toilets, are protected by P-traps that contain a small amount of standing water to prevent sewer gases from escaping. When the traps are properly filled with water, the drain pipes form a closed system, and when water flows, it creates a vacuum behind it that can slow it down or even stop it. The purpose of the vents is to allow air into the pipes to replace the displaced air so the water keeps flowing. They also provide a way for sewer gases to escape outside the house, but this purpose is secondary.
Symptoms of Poor Venting
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One effect of a drain system that isn't properly vented is that water flow becomes slower and sediments settle out, eventually blocking the pipes. You may notice this slower flow in a sink or tub drain or when you flush the toilet. Another effect of poor venting is a vacuum created by flowing water that sucks air through P-traps. Your toilet has a trap built into it and is vulnerable to this effect, especially in the presence of a large flow of water such as from a bathtub. The gurgling sound you hear is the water in the trap being displaced by air.
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The Importance of Venting
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It's important to clear the vents if you notice frequent blockages, slow water flow or gurgling coming from nearby drains when you open one to let water out. Poor venting can cause blockages that are difficult to clear. If you do clear them to allow water to flow faster, it can create a suction force large enough to empty P-traps. When the traps empty, there is nothing to prevent sewer smells from contaminating your bathroom or kitchen. The smells are not only noxious, they promote the growth of pathogens that can cause disease.
Clearing Blocked Vents
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Properly installed vents all have an upward slope and usually connect to a main vent stack that extends through the roof. Debris usually doesn't settle in them but may at places where they have a sharp change of direction. The blockage is often at the vent opening itself, where debris such as leaves can collect. Climbing on the roof and inspecting the opening will reveal the presences of such debris, which is easily removed. If the blockage is inside the pipes, you can usually clear it by spraying a jet of water into the vent opening with a garden hose. If the water backs up, clear the vent with a plumbing auger.
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References
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